import sys

def run(a,b):
    if a < 3:
        if a == 2:
            return b+1
        return b
    b = a//3 + b
    a = a//3+a%3
    return run(a,b)

for line in sys.stdin:
    _a = line.strip()
    if _a != "0":
        print(run(int(_a),0))